Tobacco smoke filter



United States Patent Ofiice 3,033,209 Patented May 8, 1962 New Jersey No Drawing. Filed Aug. 28, 1959, Ser. No. 836,588 12 Claims. ((11. 131-10) This invention relates to a new and improved filter material for tobacco smoke. In particular, it relates to a new and improved type of tissue paper for use in cigarette filters.

A wide variety of fibrous products have been disclosed as useful for the manufacture of filters for tobacco smoke, particularly as cigarette filters. Thus, products such as paper, cotton, cellulose acetate and various synthetic fibers have been suggested. However, due to processing difiiculties, cost of manufacture, poor performance, etc., some of these materials have not reached commercial stage production. Only two of these products have achieved any degree of commercial success, namely, tissue paper and cellulose acetate tow. These materials are both cheap and effective .and can be rapidly and economically converted to filters on the cigarette filter-making machinery currently in wide-spread use by the industry.

Soft tissue paper in various forms has been employed in cigarette filters, but has the serious drawback of becoming limp and soggy as the cigarette is smoked as the tissue paper absorbs water both from the smoke and from the smokers mouth. It is well known that the combustion of cigarette tobacco produces a relatively large amount of moisture vapor much of which together with the tar condenses on the filter. This, in addition to the moisture pick-up when the filter touches the smokers tongue, produces an objectionable sogginess in the case of paper filters. The soft, wet tissue paper filter is susceptible to distortion so as to allow the passage of smoke through large channels which might appear in the filter instead of uniformly through the entire filter surface. Channeling such as this reduces the effectiveness of the filter.

One object of my invention is to provide an entirely new and improved type of tissue paper for the production of smoke filters, particularly for cigarettes. Another object is to provide a tissue paper which when converted to a cigarette filter will not become soggy and distorted as the cigarette is smoked. A further object is to provide a new type of tobacco smoke filter which is highly effective for the removal of nicotine and tar from tobacco smoke. A still further object of my invention is to provide a tobacco smoke filter, the filtering element of which essentially consists of thin paper which has been partially acylated. Other objects of my invention will appear herein.

The above objects are accomplished by using as a tobacco smoke filter a thin paper which had been partially .acylated, such as by treating the paper with an aliphatic acid anhydride. The partial acylation of thin paper should be carried out in such manner that the original fine fibrous network of the paper is not altered appreciably. Hence, the acylation of the paper should be such that the cellulose retains its physical form, namely, a fibrous esterification, so as to avoid dissolution or excessive swelling of the paper in the acylation procedure.

A number of fibrous acylation techniques which involve partially esterifying cellulose Without altering the original fibrous form are known and are useful for making the partially acylated thin paper employed for making tobacco smoke filters. For instance, the thin paper may be acylated in a procedure using acetic anhydride and alkane disulfonic acid, such as methane disulfonic acid as the catalyst. For instance, the paper may be run over suction boxes in which it is first activated by pulling water through the paper, then dewatered by pulling glacial acetic acid through the paper and then acylated by pulling through the paper a mixture of 47% acetic acid, 50% acetic anhydride and 3% methane disulfcnic acid, holding the temperature at 2831 C. with the acetylation time being 10-15 seconds. Other catalysts than methane disulfonic acid may be employed to promote this acylation, such as sulfoacetic acid, toluene sulfonic acid, zinc chloride, methane trisulfonic acid, phosphoric acid or benzene disulfonic acid. Instead of a pull through, the thin paper after activation may be dipped into an acylating bath consisting of an aliphatic acid anhydride, an organic solvent diluent and a strong acid catalyst. Within several minutes at room temperature, or slightly above, the paper is partially acylated to a degree of substitution of about 1 acyl group per glucose unit and its fibrous structure and physical appearances remain the same. The acylation technique can have many variations with respect to time, temperature, choice of organic diluent, choice of catalyst and the like. The method is not limited to any certain aliphatic anhydride as the esterifying agent. Thus, acetic, propionic, butyric, isobutyric, valeric, etc., anhydride may be used and the conditions altered appropriately to compensate for the more sluggish reaction rates of the higher anhydrides. The aliphatic acid anhydride used may contain a substituent group providing that group is not hydrophilic, that is, the anhydride should not have sulfate, hydroxyl or like groups therein.

In the case of the higher acyl groups, the paper may become water resistant with the addition of less acyl thereto than where acetyl is used as the acyl group. For instance, where the paper is treated with acetic anhydride, it is desirable that a minimum acetyl content of 14% is reached corresponding to a degree of substitution of about 0.6 acetyl groups per glucose units. The acetyl content may be up to 30% without interfering With the physical structure thereof. In the case of butyration the degree of substitution most satisfactory has been found within the range of 0.3-1.2 groups per glucose unit, while with hexanoic acid the degree of substitution may be within the range of 0.1-0.9 group per glucose unit .and with octanoic acid the degree of substitution may be within the range of 005-05 group per glucose unit.

An outstanding advantage of the invention is that the thin porous paper upon partial acylation is made moisture repellent to a highly uniform degree without the air porosity of the paper being effected. Usually imparting moisture repellency to paper is characterized by a surface treatment and very little of the repellent agent is intimately mixed with the individual fibers throughout the paper. This acts to reduce the porosity of the paper. The material employed for filtering purposes in accordance with my invention, however, does not evidence a high pressure drop or resistance to draw in use as a cigarette filter as a result of the air porosity of the paper.

Very soft crepe tissue paper is particularly adapted for use for filtering tobacco smoke giving good porosity and a highly effective surface when smoke is brought into the presence of the filter. The preferred type of filter which is partially acylated for use in tobacco filters in accordance with my invention is a soft tissue paper having a thickness of 0.0010.004 inch.

The preparation of filters'in accordance with my invention involves collecting partially acylated tissue paper into a mass forming into convenient lengths and drawing into the form of a rod of suitable cross sectional diameter for use in the cigarette or any other tobacco product used for smoking.

The following examples illustrate the preparation of filters in accordance with my invention and the use of those filters in the preparation of cigarettes or other commercial products.

Example 1 Several sheets of soft tissue paper were subjected to a fibrous acetylation imparting thereto an acetyl content of 20.6% or an average degree of substitution of about 1 acetyl group per glucose unit of the cellulose. The acety lated paper reveals upon microscopic examination that it is similar in structure to the unacetylated paper employed as the starting material being a fine network of coarse and fine fibers. A 4-ply sheet, 7 x 22.5 cm. size, of the paper was given 20 folds, the folds being parallel with the width of the sheet. There was thus obtained a paper rod 70 mm. in length. The rod of folded paper was wrapped in conventional cigarette paper by passing through the garniture of a cigarette filter machine. A total of filter rods of the acetylated paper were thus prepared. Five filter rods were also prepared from the soft tissue paper, unacylated, as a control. Each set of filter rods were cut into filter tips 15 mm. in length and the tips were taped to the ends of nonfilter, regular size (70 mm.) cigarettes. When a cigarette with a non-acylated control filter was smoked by mouth, the filter became soft and wet after half of the cigarette had been consumed. It was observed that fissures started to appear in the end of the filter and that a considerable amount of the main stream smoke was passing through these openings rather than through the entire filter. When a cigarette with an acetylated paper filter was smoked by mouth the filter remained firm and undistorted through the entire smoking cycle.

Cigarettes prepared as before with the respective filters being taped thereon were automatically smoked in a machine similar in design and operation to the smoking machine described by Bradford et a1., Industrial and Engineering Chemistry, 28, 836, 1936. These tests indicated that the filters of acetylated paper removed 8% more nicotine and 10% more tar than the filters of unacetylated paper. Both types of filters had an average pressure drop of 1.5 inches at an air flow rate of 1050 ml. per minute before being tested. After the smoking tests the acetylated paper filters (tobacco butt removed) had an average pressure drop of 1.7 inches whereas the control filters had an average pressure drop of 2.2 inches. The acetylated paper filter showed a pressure drop increase of approximately 13%, whereas the control filter made of unacetylated tissue paper had an average pressure drop increase of approximately 47%.

Example 2 Several sheets of soft tissue paper of good porosity were isobutyrylated by a fibrous esterification method to an isobutyryl content of 18% being a degree of substitution of 0.5 isobutyryl groups per glucose units. The esterification did not alter the structure of the paper. Filters of ml. length were prepared from the paper in the manner described in the preceding example. These filters had a pressure drop of 1.7 inches at an air flow rate of 1050 ml. per minute. Some of these filters were attached to nonfilter, regular size cigarettes, which cigarettes were smoked by several individuals. In all cases the filters remained firm and undistorted throughout the smoking cycle. The used filters had a pressure drop of 1.8 inches, an increase of approximately 6%. Automatic smoking tests indicated the filters removed 5% more nicotine and 6% more tar than the control filters of Example 1.

Example 3 Several sheets of soft tissue paper of good porosity were esterified by a fibrous esterification method using hexanoic anhydride imparting a hexanoyl content of 17.3%, a degree of substitution of 0.3 hexanoyl groups per glucose unit. The structure of the esterified paper was not altered by the esterification. Filters were prepared by the paper in the manner described in Example 1. These filters had a pressure drop of 1.4 inches at an air flow rate of 1050 ml. per minute. Some of these filters were attached to unfiltered, regular size cirgarettes and the cigarettes were smoked by several individuals. In all cases the filter remained firm and undistorted throughout the smoking cycle. The used filters had a pressure drop of 1.6, an increase of about 14%. Tests of the cigarettes with the hexanoylated paper filters attached thereto indicated the filter removed 9% more nicotine and 6% more tar than the control filters of Example 1.

Example 4 A roll of soft tissue paper (0.002 inch thick) was fed through a Water bath onto an endless perforated stainless steel belt. The water was removed by glacial acetic acid using several countercurrent washes sucked through the paper by vacuum. Acetylation was accomplished by several pull through washes of acetylation liquor consisting of 44% acetic acid, 50% acetic anhydride and 6% benzene disulfonic acid. The temperature was held at 30 C. and the total time the paper was immersed in the acetylated bath was 18 seconds. The acetylation liquor was removed as the endless belt containing the paper was led through an acetic acid bath followed by a Water bath. The dried product contained 28% acetyl and retained of its original strength. In appearance it was no different from the starting material. A 2 inch x 2 inch square of the paper, when placed on the surface of distilled water (25 C.) in a beaker, required 3 minutes before it was thoroughly wet. The control paper was wet immediately after it was placed on the surface of the Water at 25 C.

Although this last example illustrates one method for obtaining a partially acylated paper it is understood that a number of variations of this technique can be employed. Thus, for example, the acylation can be carried out in a batchwise manner wherein the sheet of the paper is dipped in the esterifying bath consisting of the acid anhydride, its corresponding acid, and catalyst. Then the acylated paper is dipped in water or. an inert organic solvent to remove the adhering acylating mixture. The length of time the paper remains in the esterifying solution is so adjusted that it is only partly esterified. It is not esterified to the point where it becomes soluble in the mixture. If desired, inert diluents (toluene for example) could be added to the esterifying bath to prevent the paper from dissolving should it be overexposed to the solution. Such techniques for esterifying cellulose in its original fibrous form are well known to the art. Finally, it is understood that it is also possible to esterify raw cellulose fibers by a batch technique and then convert these fibers into the form of a paper sheet by the usual paper making techniques or a slight modification thereof. Such papers will also have the.desired properties if their acyl contents are within the ranges specified.

I claim:

1. A tobacco smoke filter, the filtering portion of which essentially consists of a mass of thin porous paper, the cellulose of which paper has been fibrously and partially acylated with the anhydride of a lower fatty acid until it contains 0.1 to 1.5 chemically bound acyl groups per glucose unit of its structure.

2. A tobacco smoke filter according to claim 1 in which the paper thereof is in crimped form.

3. A tobacco smoke filter according to claim 1 in which the paper thereof is a creped tissue paper.

4. A smoke filtering element characterized by retention of its physical form and porosity when moist and which is resistant to sogginess which comprises a mass of thin porous paper in rod form, the cellulose of which paper has been fibrously and partially acylated with the anhydride of a lower fatty acid until it contains 0.1 to 1.5 chemically bound acyl groups per glucose unit of its structure.

5. A cigarette comprising a tobacco cylinder, a filter cylinder adjacent one end of the tobacco cylinder and a cigarette paper wrapped around the filter cylinder and the tobacco cylinder, said filter cylinder comprising a mass of thin porous paper, the cellulose of which has been fibrously and partially acylated with the anhydride of a lower fatty acid until it contains 0.1 to 1.5 chemically bound acyl groups per glucose unit of its structure, the paper being capable of permanently retaining its physical form and porosity in either a dry or wet condition.

6. A cigarette according to claim 5 in which the paper of the filter cylinder is crimped parallel to the longitudinal axis of the filter.

7. A cigarette according to claim 5 in which the paper of the filter cylinder is a creped tissue paper.

8. A cigarette according to claim 5 in which the paper of the filter cylinder has been fibrously acetylated to an acetyl content of 14-30%.

9. A cigarette according to claim 5 in which the paper of the filter cylinder is tissue paper, which has been fibrously and partially acetylated to an acetyl content of 6 l430% and then crimped parallel to the longitudinal axis of the filter.

10. A small rod of tissue paper, which had been fibrously partially acetylated to an acetyl content of 14- and then crimpe'd parallel to the longitudinal axis of the rod.

11. A process for the purification of tobacco smoke from a smoking article which comprises passing said smoke through a filter comprising a mass of thin porous paper, the cellulose of which paper has been fibrously and partially acylated to an acetyl content of 14-30%.

12. A process according to claim 11 wherein the filter comprises a mass of tissue paper which has been fibrously partially acetylated to an acetyl content of 14-30% and then crimped parallel to the longitudinal axis of the filter.

References Cited in the file of this patent UNITED STATES PATENTS 1,338,529 Richter Apr. 27, 1920 2,164,702 Davidson July 4, 1939 2,228,383 Berl Jan. 14, 1941 2,253,724 New et al Aug. 26, 1941 2,806,474 Yarsley Sept. 17, 1957 2,887,429 Griggs et al May 19, 1959 

1. A TOBACCO SMOKE FILTER, THE FILTERING PORTION OF WHICH ESSENTIALLY CONSISTS OF A MASS OF THIN POROUS PAPER, THE CELLULOSE OF WHICH PAPER HAS BEEN FIBROUSLY AND PARTIALLY ACYLATED WITH THE ANHYDRIDE OF A LOWER FATTY ACID UNTIL IT CONTAINS 0.1 TO 1.5 CHEMICALLY BOUND ACYL GROUPS PER GLUCOSE UNIT OF ITS STRUCTURE. 